The present invention relates generally to monitoring physiological characteristics and, more particularly, to measuring dermal hydration.
It can be useful in a variety of situations to monitor physiological characteristics. For example, an instrument for detecting and measuring physiological changes that accompany emotional stress is commonly referred to as a polygraph. A polygraph typically includes multiple sensors that are directly connected to an individual""s body for measuring multiple physiological parameters. Standard polygraph sensors include a blood pressure cuff, a pair of respiration belts, and skin resistance finger electrodes, all of which are coupled to data collection and recordation equipment.
The skin resistance finger electrodes of a polygraph are used to measure galvanic skin response (GSR). GSR reflects the emotional stress level of the individual being tested by providing a measure of skin conductivity or resistance, which is largely influenced by sweat gland activity. The sweat glands secrete perspiration that flows to the surface of the skin. The perspiration includes liquid and electrolytes; therefore, perspiration facilitates electrolytic conduction at the surface of the skin. GSR testing typically includes attaching electrodes to separate fingers of the same hand and attaching a galvanometer to the electrodes to measure the conductance or resistance between the electrodes.
Having to attach electrodes to an individual to measure their GSR can be disadvantageous is some circumstances. The electrodes are invasive, and therefore they can be uncomfortable to the individual being examined and can themselves cause the individual being tested to become stressed. The invasive and stressful nature of conventional GSR testing can disadvantageously contribute to people""s hesitance to being subjected to GSR and polygraph examinations, and to some degree also complicates the interpretation of the results of such examinations.
Another technique for monitoring physiological characteristics is disclosed in U.S. Pat. No. 5,867,257 to Rice et al., which is incorporated herein by reference. The Rice et al. patent discloses a battlefield personnel threat detection system for identifying and analyzing vibrations, such as vibrations caused by the heartbeat of an animal. More specifically, a micro-doppler ladar beam is transmitted, scattered back, collected and analyzed. Whereas such use of a micro-doppler ladar provides for noninvasive monitoring of physiological characteristics, it does not lend itself to GSR-like measurements.
Accordingly, there is a need in the art for methods and apparatus that are capable of at least generally noninvasively monitoring a physiological characteristic and that can at least potentially serve as surrogates for GSR testing.
The present invention solves the above and other problems by providing methods and apparatus that utilize electromagnetic radiation in the furtherance of determining dermal hydration. In accordance with one aspect of the present invention, measurements of dermal hydration can serve as surrogates for GSR measurements.
In accordance with one aspect of the present invention, dermal hydration is determined in a target region of a human subject by determining a relationship between first and second measurements. The first and second measurements are measurements of electromagnetic radiation that has been reflected from the target region. In accordance with one embodiment, the first measurement is a measurement of a first type of electromagnetic radiation that has been reflected from the target region, and the second measurement is a measurement of a second type of electromagnetic radiation that has been reflected from the target region. To detect and measure dermal hydration, the second type of electromagnetic radiation is absorbed by liquid, namely water or more specifically perspiration, to a greater degree than the first type of electromagnetic radiation is absorbed by the liquid.
In accordance with one aspect of the present invention, the electromagnetic radiation that is reflected from the target region and measured is initially transmitted to the target region from a remote location, and the transmitted electromagnetic radiation, such as a laser beam, is not visible to a naked human eye. In accordance with one aspect of the present invention, dermal hydration of a target region is determined while the target region is moving, by tracking the target region. As a result, examinations carried out in accordance with the present invention can advantageously be generally noninvasive and remotely administered, and the subject being examined need not even be aware of the examination.